<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <script src="../../vue.js"></script>
</head>

<body>
  <div id="app">
    <ul>
      <li v-for='c in products'>
        <input v-model="c.quantity" type="text">
        {{c.name}}</li>
    </ul>
    <span>{{total}}</span>
  </div>

</body>
<script>

  var vm = new Vue({
    el: '#app',
    data: {
      products: []
    },
    computed: {
      total() {
        return this.products.reduce((total, obj) => {
          return total += parseInt(obj.quantity);
        }, 0)
      }
    },
    mounted() {
      //https://api.myjson.com/bins/1h8gwt
      fetch('https://api.myjson.com/bins/1h8gwt')
        .then((res) => res.json())
        .then((json) => {
          this.products = json.products;
        })
    }
  })



</script>

</html>